Purpose – The purpose of this paper is to examine how clothing retail buyers (i.e., retail buyers, merchandisers, and storeowners), who are involved in assortment planning and retail buying use assortment criteria in their decisions. Comparisons are made between criteria used by men’s wear and women’s wear retail buyers as well as criteria used by male and female retail buyers. Research design, data, and methodology – A structured questionnaire was developed to collect data both in English and Korean. After conducting two pilot tests, the survey was conducted in Seoul, South Korea. Mantrala et al.’s 17 inputs of product assortment planning model with 23 assortment criteria from other previous studies were used. Results – Significant differences existed in consideration of assortment criteria between men’s wear and women’s wear retail buyers as well as between male and female retail buyers. Men’s wear retail buyers rated the importance of sales history criteria (i.e., sales history, previous year’s sales of same/similar styles) significantly lower than women’s wear buyers did. Female retail buyers rated sales history criteria and weather criteria (i.e., unpredicted weather change, forecasting information of weather) significantly higher than male retail buyers did. Conclusions – This study provides guidelines for retail buyers regarding what criteria to use in what situations and how to organize assortment criteria from the most important criterion to the least one. In addition, the findings help them understand other retail buyers’ buying behavior.